Method, apparatus, and program for judging grid quality

ABSTRACT

An image obtaining section obtains a radiation image that includes a periodic pattern of a grid. A frequency analyzing section performs frequency analysis on the radiation image to obtain a frequency spectrum of the radiation image. A peak determining section determines a peak within the frequency spectrum to be a target of processing. A first judging section measures the width of the peak which is the target of processing, and judges the quality of the grid based on the measured width of the peak.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to JapanesePatent Application No. 2015-224672 filed on Nov. 17, 2015. The aboveapplication is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND

The present invention is related to a grid quality judging apparatus, agrid quality judging method, and a grid quality judging program forjudging the quality of a scattered ray removing grid or for generatingquality data that represents the quality of the scattered ray removinggrid, which is utilized in cases that radiation images are obtained,that removes the influence of scattered rays scattered by a subject.

When obtaining a radiation image of a subject formed by radiation whichhas passed through the subject, scattered rays are generated within thesubject, particularly when the thickness of a subject is great.Conventionally, there is a problem that these scattered rays decreasethe contrast of the obtained radiation image. For this reason, there arecases in which a scattered ray removing grid (hereinafter, simplyreferred to as “grid”) is provided between the subject and a radiationdetector for detecting radiation to obtain a radiation image such thatthe scattered rays are not irradiated onto the radiation detector whenperforming imaging. If imaging is performed employing the grid,radiation which is scattered by the subject becomes less likely to beirradiated onto the radiation detector, and thereby the contrast of anobtained radiation image can be improved.

A grid is constituted by alternately arranging lead or the like, whichdoes not transmit radiation, and an interspace material such asaluminum, fiber, etc., which readily transmits radiation, at a fine griddensity of approximately 4 lines/mm, for example. For this reason,periodic patterns caused by the grid, such as periodic stripes and moirepatterns, are generated within radiation images when the grid isemployed to perform imaging, resulting in the radiation images becomingdifficult to view. Note that a moire pattern is a fine periodic patternwhich is generated in the case that the grid density is greater than theNyquist frequency of a radiation image.

For this reason, various techniques have been proposed to obtain images,of which observation is facilitated, in which periodic patterns arereduced by administering filtering processes to remove the frequencycomponents of periodic patterns (refer to Japanese Unexamined PatentPublication No. 2002-152467).

There are cases in which there are fluctuations in the grid density ofgrids, which is the number of stripes per unit length, due tomanufacturing error and deterioration over time. For this reason, atechnique has been proposed, in which interval defects of grids aredetected by performing imaging while varying the orientation of thegrids, then detecting the interval defects based on the signal strengthsof grid images obtained by the imaging operations (refer to JapaneseUnexamined Patent Publication No. S61(1986)-133848).

SUMMARY

In the case that the aforementioned fluctuations in grid density arepresent, unnecessary periodic structures which differ from the intendedperiodic structure of the grid will be included within the grid. Inaddition, there are also cases in which the influence of adhesive agentsthat adhesively attach the materials that constitute the grid causeunnecessary periodic structures different from the intended periodicstructure of the grid to be included, in addition to the fluctuations ingrid density. Further, the surface of the grid is polished duringproduction thereof. There are cases in which streaks due to polishingare generated in directions different from the direction of the stripesof the grid, and these streaks cause unnecessary periodic structures tobe included as well. The frequencies of such unnecessary periodicstructures are different from the frequency of the intended periodicstructures of the grid. For this reason, even if filtering processes areadministered to remove frequency components of more patterns which aregenerated due to a grid from a radiation image which is obtained byperforming imaging employing the grid, it is not possible to removefrequency components that correspond to the unnecessary periodicstructures from the radiation image. Frequency components correspondingto such unnecessary periodic structures that cannot be removed become ahindrance to diagnosis employing the radiation image. Accordingly, it ispreferable for a judgment to be rendered regarding whether a grid is ofa utilizable quality when performing imaging utilizing a grid, and toutilize only grids having utilizable qualities.

Interval defects of a grid can be detected if the technique disclosed inJapanese Unexamined Patent Publication No. S61(1986)-133848 is employed,and therefore whether a grid is of a utilizable quality can be judged.However, it is necessary to perform a plurality of imaging operationswhile changing the orientation of a grid and a plurality of analyses ofsignal strengths in the technique disclosed in Japanese UnexaminedPatent Publication No. S61(1986)-133848. Therefore, a long amount oftime is required for the process of judging the quality of a grid.

The present disclosure has been developed based on the foregoingcircumstances. The present disclosure enables the quality of a grid tobe judged easily.

A first grid quality judging apparatus of the present disclosurecomprises:

a frequency analyzing means for performing frequency analysis on aradiation image that includes a periodic pattern caused by a grid, toobtain a frequency spectrum of the radiation image; and

a judging means for judging the quality of the grid, based on peakswhich are included in the frequency spectrum.

Note that in the first grid quality judging apparatus of the presentdisclosure, the judging means may measure the widths of the peaks andjudge the quality of the grid based on the measured widths of the peaks.

In addition, the first grid quality judging apparatus of the presentdisclosure may further comprise a peak determining means for determiningpeaks within the frequency spectrum which will be targets of processing,and the judging means may measure the widths of the peaks which are thetargets of processing and judge the quality of the grid based on themeasured widths of the peaks which are the targets of processing.

In addition, in the first grid quality judging apparatus of the presentdisclosure, the frequency analyzing means may divide the radiation imageinto a plurality of regions and obtain frequency spectra for each of theplurality of regions, and the judging means may measure the widths ofpeaks within each of the plurality of regions, and judge the quality ofthe grid in each of the plurality of grids based on the measured widthsof the peaks within each of the plurality of regions.

In addition, in the first grid quality judging apparatus of the presentdisclosure, the frequency analyzing means may divide the radiation imageinto a plurality of regions and obtain frequency spectra for each of theplurality of regions, the peak determining means may determine peaks tobe targets of processing within each of the plurality of regions, andthe judging means may measure the widths of peaks which are targets ofprocessing within each of the plurality of regions, and judge thequality of the grid in each of the plurality of regions based on themeasured widths of the peaks which are targets of processing within eachof the plurality of regions.

In the frequency spectrum, the greatest peak will appear at thefrequency having the intended periodic structure of the grid. The “peakswhich are to be targets of processing” may be determined to be thefrequency having the greatest peak within the frequency spectrum, or maybe determined by receiving specification of peaks which are to betargets of processing within the frequency spectrum.

In addition, the first grid quality judging apparatus of the presentdisclosure may further comprise a harmonic frequency calculating meansfor calculating the frequency of at least one harmonic which isgenerated based on the grid density and the Nyquist frequency of theradiation image, and the judging means may compare the frequency of thepeaks within the frequency spectrum and the frequency of the at leastone harmonic, and judge the quality of the grid based on the presence orthe absence of a peak at a frequency different from the frequency of theharmonic.

In this case, the frequency analyzing means may divide the radiationimage into a plurality of regions and obtain frequency spectra for eachof the plurality of regions, the harmonic frequency calculating meansmay calculate the frequency of at least one harmonic within each of theplurality of regions, and the judging means may compare the frequency ofthe peaks within the frequency spectrum and the frequency of the atleast one harmonic, and judge the quality of the grid based on thepresence or the absence of a peak at a frequency different from thefrequency of the harmonic within each of the plurality of regions.

In addition, in the first grid quality judging apparatus of the presentdisclosure, the frequency analyzing means may obtain frequency spectrafor each of a first and second direction which are perpendicular to eachother, by performing frequency analysis in the first and seconddirections within the radiation image, the first grid quality judgingapparatus may further comprise a peak presence detecting means fordetecting the presence or absence of peaks within the frequency spectrafor the first and second directions, and the judging means may judge thequality of the grid based on the presence or absence of peaks within thefrequency spectra for the first and second directions.

In this case, the frequency analyzing means may divide the radiationimage into a plurality of regions and obtain frequency spectra for thefirst and second directions within each of the plurality of regions, thepeak presence detecting means may detect the presence or absence ofpeaks within the frequency spectra of each of the plurality of regions,and the judging means may judge the quality of the grid based on thepresence or absence of peaks within the frequency spectra for the firstand second directions within each of the plurality of regions.

A second grid quality judging apparatus of the present disclosurecomprises:

a frequency analyzing means for performing frequency analysis on aradiation image that includes a periodic pattern caused by a grid, toobtain a frequency spectrum of the radiation image;

a quality data generating means that generates quality data thatrepresents the quality of the grid, based on peaks which are included inthe frequency spectrum; and

a display means for displaying the quality data.

The “quality data” refers to data that enables those who view thedisplayed quality data to judge the quality of the grid. Specificexamples of the quality data include: the widths of peaks which aretargets of processing within the frequency spectrum to be describedlater; the presence or absence of peaks at frequencies different fromthat of a harmonic frequency; and the presence or absence of peakswithin frequency spectra for a first and second direction which areperpendicular to each other within the radiation image.

Note that in the second grid quality judging apparatus of the presentdisclosure, the quality data generating means may measure the widths ofthe peaks and generate the quality data based on the measured widths ofthe peaks.

In addition, the second grid quality judging apparatus of the presentdisclosure may further comprise a peak determining means for determiningpeaks within the frequency spectrum which will be targets of processing,and the quality data generating means may measure the widths of thepeaks which are the targets of processing and generate the quality databased on the measured widths of the peaks which are the targets ofprocessing.

In addition, in the second grid quality judging apparatus of the presentdisclosure, the frequency analyzing means may divide the radiation imageinto a plurality of regions and obtain frequency spectra for each of theplurality of regions, and the quality data generating means may measurethe widths of peaks within each of the plurality of regions, andgenerate the quality data for each of the plurality of grids based onthe measured widths of the peaks within each of the plurality ofregions.

In addition, in the second grid quality judging apparatus of the presentdisclosure, the frequency analyzing means may divide the radiation imageinto a plurality of regions and obtain frequency spectra for each of theplurality of regions, the peak determining means may determine peaks tobe targets of processing within each of the plurality of regions, andthe quality data generating means may measure the widths of peaks whichare targets of processing within each of the plurality of regions, andgenerate the quality data for each of the plurality of regions based onthe measured widths of the peaks which are targets of processing withineach of the plurality of regions.

In addition, the second grid quality judging apparatus of the presentdisclosure may further comprise a harmonic frequency calculating meansfor calculating the frequency of at least one harmonic which isgenerated based on the grid density and the Nyquist frequency of theradiation image, and the quality data generating means may compare thefrequency of the peaks within the frequency spectrum and the frequencyof the at least one harmonic, and generate the quality data based on thepresence or the absence of a peak at a frequency different from thefrequency of the harmonic.

In this case, the frequency analyzing means may divide the radiationimage into a plurality of regions and obtain frequency spectra for eachof the plurality of regions, the harmonic frequency calculating meansmay calculate the frequency of at least one harmonic within each of theplurality of regions, and the quality data generating means may comparethe frequency of the peaks within the frequency spectrum and thefrequency of the at least one harmonic, and generate the quality databased on the presence or the absence of a peak at a frequency differentfrom the frequency of the harmonic within each of the plurality ofregions.

In addition, in the second grid quality judging apparatus of the presentdisclosure, the frequency analyzing means may obtain frequency spectrafor each of a first and second direction which are perpendicular to eachother, by performing frequency analysis in the first and seconddirections within the radiation image, the second grid quality judgingapparatus may further comprise a peak presence detecting means fordetecting the presence or absence of peaks within the frequency spectrafor the first and second directions, and the quality data generatingmeans may generate the quality data based on the presence or absence ofpeaks within the frequency spectra for the first and second directions.

In this case, the frequency analyzing means may divide the radiationimage into a plurality of regions and obtain frequency spectra for thefirst and second directions within each of the plurality of regions, thepeak presence detecting means may detect the presence or absence ofpeaks within the frequency spectra of each of the plurality of regions,and the quality data generating means may generate the quality databased on the presence or absence of peaks within the frequency spectrafor the first and second directions within each of the plurality ofregions.

A first grid quality judging method of the present disclosure comprises:

performing frequency analysis on a radiation image that includes aperiodic pattern caused by a grid, to obtain a frequency spectrum of theradiation image; and

judging the quality of the grid, based on peaks which are included inthe frequency spectrum.

A second grid quality judging method of the present disclosurecomprises:

performing frequency analysis on a radiation image that includes aperiodic pattern caused by a grid, to obtain a frequency spectrum of theradiation image;

generating quality data that represents the quality of the grid, basedon peaks which are included in the frequency spectrum; and

displaying the quality data.

The first and second grid quality judging methods of the presentdisclosure may be provided as programs to be executed by a computer.

According to the first grid quality judging apparatus, the first gridquality judging method, and the first grid quality judging program ofthe present disclosure, frequency analysis is performed on a radiationimage that includes a periodic pattern caused by a grid, to obtain afrequency spectrum of the radiation image. Then, the quality of the gridis judged, based on peaks which are included in the frequency spectrum.Here, the manner in which the peaks which are included in the frequencyspectrum appear will differ depending on the presence or absence ofunnecessary periodic structures which are different from the intendedperiodic structure of the grid. The first grid quality judgingapparatus, the first grid quality judging method, and the first gridquality judging program of the present disclosure are capable of judgingthe presence or absence of periodic structures which are unnecessary inthe grid, based on the peaks which are included within the frequencyspectrum. Accordingly, the quality of the grid can be judged easily,only by performing imaging employing the grid.

According to the second grid quality judging apparatus, the second gridquality judging method, and the second grid quality judging program ofthe present disclosure, frequency analysis is performed on a radiationimage that includes a periodic pattern caused by a grid, to obtain afrequency spectrum of the radiation image. Then, quality data thatrepresents quality of the grid is generated, based on peaks which areincluded in the frequency spectrum, and the quality data is displayed.Here, the manner in which the peaks which are included in the frequencyspectrum appear will differ depending on the presence or absence ofunnecessary periodic structures which are different from the intendedperiodic structure of the grid. The second grid quality judgingapparatus, the second grid quality judging method, and the second gridquality judging program of the present disclosure enable the presence orabsence of periodic structures which are unnecessary in the grid to bejudged, based on the peaks which are included within the frequencyspectrum. Accordingly, the quality of the grid can be judged easily,only by performing imaging employing the grid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that schematically illustrates theconfiguration of a radiation imaging system to which a grid qualityjudging apparatus according to a first embodiment of the presentdisclosure is applied.

FIG. 2 is a diagram that illustrates the schematic structure of the gridquality judging apparatus according to the first embodiment.

FIG. 3 is a diagram for explaining frequency analysis which is performedby the first embodiment.

FIG. 4 is a diagram that illustrates a frequency spectrum.

FIG. 5 is a diagram that illustrates a grid having fluctuations in thegrid density thereof.

FIG. 6 is a diagram that illustrates a frequency spectrum for a case inwhich fluctuations in grid density are present.

FIG. 7 is a flow chart that illustrates the processes which areperformed by the first embodiment.

FIG. 8 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to a second embodiment.

FIG. 9 is a diagram that illustrates a grid in which a periodicstructure different from the intended structure of the grid is present.

FIG. 10 is a diagram that illustrates a frequency spectrum for a case inwhich a periodic structure different from the intended structure of agrid is present.

FIG. 11 is a flow chart that illustrates the processes which areperformed by the second embodiment.

FIG. 12 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to a third embodiment.

FIG. 13 is a diagram for explaining frequency analysis which isperformed by the third embodiment.

FIG. 14 is a diagram that illustrates a frequency spectrum in thedirection of the stripes of a grid.

FIG. 15 is a diagram that illustrates a grid that includes a periodicstructure in a direction different from that of the strips of a grid.

FIG. 16 is a diagram that illustrates a frequency spectrum for a case inwhich a grid includes a periodic structure in a direction different fromthat of the strips of the grid.

FIG. 17 is a flow chart that illustrates the processes which areperformed by the third embodiment.

FIG. 18 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to a fourth embodiment.

FIG. 19 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to a fifth embodiment.

FIG. 20 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to a sixth embodiment.

FIG. 21 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to a seventh embodiment.

FIG. 22 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to an eighth embodiment.

FIG. 23 is a diagram that illustrates quality data which is displayed bya display unit in the eighth embodiment.

FIG. 24 is a flow chart that illustrates the processes which areperformed by the eighth embodiment.

FIG. 25 is a diagram that illustrates an alternate example of qualitydata which is displayed on the display unit in the eighth embodiment.

FIG. 26 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to a ninth embodiment.

FIG. 27 is a diagram that illustrates quality data which is displayed bya display unit in the ninth embodiment.

FIG. 28 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to a tenth embodiment.

FIG. 29 is a diagram that illustrates quality data which is displayed bya display unit in the tenth embodiment.

FIG. 30 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to an eleventh embodiment.

FIG. 31 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to a twelfth embodiment.

FIG. 32 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to a thirteenth embodiment.

FIG. 33 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to a fourteenth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be describedwith reference to the attached drawings. FIG. 1 is a block diagram thatschematically illustrates the configuration of a radiation imagingsystem to which a grid quality judging apparatus according to a firstembodiment of the present disclosure is applied. As illustrated in FIG.1, the radiation imaging system of the present embodiment images aradiation image of a grid and performs a process of judging the qualityof the grid employing the radiation image, and is constituted by: animaging apparatus 1, and a computer 2 having the grid quality judgingapparatus according to the present embodiment installed therein.

The imaging apparatus 1 is equipped with: an X ray source 3 thatirradiates X rays as radiation onto a subject H illustrated by brokenlines during imaging of the subject H; and a radiation detector 5 thatdetects the X rays which have passed through the subject H and obtains aradiation image G0 of the subject H. In addition, during imaging of thesubject H, a scattered ray removing grid 4 (hereinafter, simply referredto as “grid 4”) for removing scattered rays which are scattered by thesubject H is provided between the subject H and the radiation detector5.

The grid 4 is constituted by alternately arranging lead or the like,which does not transmit radiation, and an interspace material such asaluminum, fiber, etc., which readily transmits radiation, at a fine griddensity of approximately 4 lines/mm, for example.

The radiation detector 5 is capable of repeatedly recording and readingout radiation images. A direct type radiation detector that directlyreceives irradiation of radiation and generates electrical charges maybe employed, or an indirect type radiation detector that temporarilyconverts radiation to visible light and converts the visible light toelectrical signals may be employed. In addition, it is desirable for thereadout method to be the TFT readout method, which reads out radiationimage signals by turning TFT's (Thin Film Transistors) ON and OFF, orthe optical readout method, which reads out radiation images byirradiating readout light. However, the readout method is not limited tothese methods, and other methods may be employed.

Note that in the present embodiment, a radiation image G0 which isobtained by imaging the subject H may be employed to judge the qualityof the grid. However, the X ray source 3 is driven, radiation which haspassed through the grid 4 is detected by the radiation detector 5, and aradiation image G0 of the grid 4 is obtained without positioning thesubject H, in order to judge the quality of the grid more accurately.

A display unit 6 and an input unit 8 are connected to the computer 2.The display unit 6 is constituted by a CRT (Cathode Ray Tube), a liquidcrystal display, or the like, and assists in various types of inputwhich are necessary for processing radiation images obtained by imagingand for processes to be performed by the computer 2. The input unit 8 isconstituted by a keyboard, a mouse, a touch panel, or the like.

A grid quality judging program of the present embodiment is installed inthe computer 2. In the present embodiment, the computer may be a workstation or a personal computer which is directly operated by anoperator, or may be a server computer connected to the work station orthe personal computer via a network. The grid quality judging program isrecorded on recording media such as a DVD (Digital Versatile Disc) and aCD-ROM (Compact Dick Read Only Memory) which are distributed, andinstalled onto the computer from the recording medium. Alternatively,the grid quality judging program is stored in a recording device of aserver computer connected to a network or in a network storage, in astate accessible from the exterior, downloaded to the computer accordingto a request, then installed therein.

FIG. 2 is a diagram that illustrates the schematic structure of the gridquality judging apparatus according to the first embodiment, which isrealized by installing the grid quality judging program in the computer2. As illustrated in FIG. 2, the grid quality judging apparatus isequipped with a CPU (Central Processing Unit) 21, a memory 22, and astorage 23, as components of a standard computer.

The storage 23 is constituted by a hard disk or a solid state drive(SSD), and has various types of data stored therein, including programsfor driving each component of the imaging apparatus 1 and the gridquality judging program. In addition, radiation images which areobtained by imaging are also stored in the storage 23.

The programs and the like which are stored in the storage 23 aretemporarily stored in the memory 22 in order for various processes to beexecuted by the CPU 21. The grid quality judging program defines animage obtaining process that causes the imaging apparatus 1 to performimaging to obtain a radiation image G0 of the grid 4, a frequencyanalyzing process that performs frequency analysis on the radiationimage G0 to obtain a frequency spectrum of the radiation image G0, apeak determining process that determines peaks which are to be target ofprocessing within the frequency spectrum, and a judging process thatjudges the quality of the grid based on the peaks which are included inthe frequency spectrum, as processes to be executed by the CPU 21.

The computer 2 functions as an image obtaining unit 31, a frequencyanalyzing unit 32, a peak determining unit 33, and a first judging unit34, by the CPU 21 executing these processes according to the gridquality judging program. Note that the computer 2 may be equipped withprocessors that respectively perform the image obtaining process, thefrequency analyzing process, the peak determining process, and thejudging process.

The imaging obtaining unit 31 obtains the radiation image G0 by imagingthe grid 4. That is, the image obtaining unit 31 drives the X ray source3 to irradiate X rays onto the grid 4, the radiation detector 5 detectsX ray which have passed through the grid 4, and obtains the radiationimage G0. Note that a program separate from the grid quality judgingprogram may obtain the radiation image G0 and store the radiation imageG0 in the storage 23. In this case, the image obtaining unit 31 readsout the radiation image G0 which is stored in the storage 23, for imageprocessing.

The frequency analyzing unit 32 performs frequency analysis on theradiation image G0 by Fourier transform or high speed Fourier transform,to obtain the frequency spectrum of the radiation image G0. FIG. 3 is adiagram for explaining the frequency analyzing process which isperformed in the first embodiment. As illustrated in FIG. 3, in the casethat the stripes of the grid 4 are parallel to the long side of theradiation detector 5 during imaging, a periodic pattern which isarranged at equidistant intervals in the direction parallel to the longside, that is, the x direction in FIG. 3, is included in the radiationimage G0. The frequency analyzing unit 32 performs frequency analysis ina direction perpendicular to the periodic pattern to obtain thefrequency spectrum. At this time, frequency spectra are calculated for aplurality of linear regions as indicated by the arrows 40 in FIG. 3, theplurality of frequency spectra obtained in each of these regions areaveraged, and ultimately obtained as the frequency spectrum. Note thatin the case that the subject H is included in the radiation image G0, itis preferable for the frequency analysis to be performed while avoidingthe region in which the subject H is present.

FIG. 4 is a diagram that illustrates the frequency spectrum. Note thatin the frequency response of FIG. 4, the horizontal axis representsfrequency (cycles/mm) and the vertical axis represents the intensity ofresponse. As illustrated in FIG. 4, the frequency spectrum has peaks atfrequencies corresponding to the intended periodic structure of thegrid. Specifically, three peaks P1, P2, and P3 are present at a firstharmonic, which has the greatest peak in response, a second harmonic,and a third harmonic. The frequencies of the second harmonic and thethird harmonic are generally higher than the frequency of the firstharmonic. However, in the case that the frequencies of the secondharmonic and the third harmonic are greater than the Nyquist frequency,the frequencies are folded back and become lower than the frequency ofthe first harmonic. In FIG. 4, the frequencies of both the secondharmonic and the third harmonic are lower than that of the firstharmonic due to this fold back phenomenon.

The peak determining unit 33 determines the peak which will be thetarget of the process for judging the quality of the grid from withinthe frequency response obtained by the frequency analyzing unit 32.Specifically, the peak determining unit 33 determines the peak havingthe greatest response as the peak which is the target of processing.Note that the peak having the greatest response within the frequencyresponse appears at the frequency of the first harmonic. For thisreason, input of the frequency of the first harmonic may be receivedfrom the input unit 8, and the peak at the input frequency of the firstharmonic may be determined to be the target of processing.

Here, the grid density of the grid 4 is known. In addition, the samplinginterval of the radiation image G0 is known, and accordingly, theNyquist frequency of the radiation image G0 is also known. In the casethat the grid density is less than or equal to the Nyquist frequency,the frequency of the first harmonic is equal to the grid density. Forthis reason, the grid density may be input as the frequency of the firstharmonic in this case. Meanwhile, in the case that the grid density isgreater than the Nyquist frequency, responses at the higher frequencyside are folded back to the lower frequency side. Therefore, thefrequency of the first harmonic is calculated by Formula (1) below, andthe calculated frequency of the first harmonic may be input. Note thatF1 is the frequency of the first harmonic, Fn is the Nyquist frequency,N is the grid density, and a is an arbitrary integer that includes 0.Note that the grid density and the Nyquist frequency of the radiationimage G0 may be stored in the storage 23, the peak determining unit 33may read out the grid density and the Nyquist frequency of the radiationimage G0, perform calculation employing Formula (1) to calculate thefrequency of the first harmonic, and the peak to be the target ofprocessing may be determined from the calculated frequency of the firstharmonic.

F1=N−2*a*Fn (in the case that (2*a+1)*Fn>N>2*a*Fn)

F1=2*(a+1)*Fn−N (in the case that 2*(a+1)*Fn>N>(2*a+1)*F)   (1)

The first judging unit 34 measures the width of the peak which isdetermined to be the target of processing, and judges the quality of thegrid 4 based on the measured width of the peak which is the target ofprocessing. Here, if there are no fluctuations in the grid density, apeak will only appear at a frequency that corresponds to the intendedperiodic structure of the grid, and therefore the width of the peakwhich is the target of processing will be small. On the other hand, inthe case that there are fluctuations in the grid density at certainpositions in the grid 4 as in the grid illustrated in FIG. 5, peaks willappear at frequencies different from the frequency of the intendedperiodic structure of the grid, in addition to the peak at the frequencyof the intended periodic structure of the grid. In addition, these twofrequencies will not differ greatly, and the values thereof will becomparatively close. As a result, the peaks of the two frequencies willoverlap, and the width of the peak which is the target of processingwithin the frequency response will become great.

That is, in the case that there are no fluctuations in grid density, thewidth of the peak having the greatest response, which is the target ofprocessing, will be L0, as illustrated in FIG. 4. Note that in thepresent embodiment, a half value at full width is obtained as the widthof the peak. Alternatively a half value at half width may be obtained asthe width of the peak. On the other hand, in the case that there arefluctuations in the grid density, a peak will also appear at a frequencyclose to the frequency of the peak that corresponds to the intendedperiodic structure of the grid, as illustrated in FIG. 6. For thisreason, the two peaks will overlap, and the width L1 of the overlappedpeaks will be greater than the width L0 illustrated in FIG. 4. Note thatin the case that peaks overlap as illustrated in FIG. 6, the half valueat full width of one of the peaks may be obtained, or the half value atfull width of the response at an average positon of the frequencies ofthe two peaks may be obtained. In FIG. 6, the half value at full widthof the response at an average positon of the frequencies of the twopeaks is obtained as the width L1 of the peak which is the target ofprocessing.

As described above, the width of the peak which is the target ofprocessing corresponds to the size of the fluctuations in grid density.That is, the fluctuations in grid density will become smaller as thewidth of the peak is smaller. For this reason, the first judging unit 34measures the width of the peak which is the target of processing withinthe frequency response, and judges the quality of the grid based on themeasured width of the peak. Specifically, the first judging unit 34compares the width of the peak which is the target of processing with athreshold value Th1, and judges the quality of the grid to be poor ifthe width of the peak which is the target of processing is greater thanor equal to the threshold value Th1. On the other hand, the judging unit34 judges the quality of the grid to be good if the width of the peakwhich is the target of processing is less than the threshold value Th1.The judging unit 34 outputs the judgment results to the display unit 6.Note that the judgment results may be any display that notifies thequality of the grid to an operator. For example, text reading NG (NoGood) in the case that the quality of the grid is poor and OK in thecase that the quality of the grid is good, or display of colorsaccording to the quality of the grid may be employed.

Next, the processes which are performed by the first embodiment will bedescribed. FIG. 7 is a flow chart that illustrates the processes whichare performed in the first embodiment. First, imaging of the grid 4 isperformed and the image obtaining nit 31 of the computer 2 obtains aradiation image G0 (step ST1). Then, the frequency analyzing unit 32performs frequency analysis on the radiation image G0 and obtains thefrequency spectrum of the radiation image G0 (step ST2). Next, the peakdetermining unit 33 determines the peak which will be a target ofprocessing within the frequency spectrum (step ST3). Then, the firstjudging unit 34 measures the width of the peak which is the target ofprocessing, judges the quality of the grid 4 (step ST4), and the processends. The judgment results are displayed by the display unit 6.

As described above, the first embodiment measures the width of the peakwhich is determined to be the target of processing within the frequencyspectrum, and judges the quality of the grid based on the measured widthof the peak. Therefore, the quality of the grid related to fluctuationsin grid density can be easily judged.

Note that in the first embodiment, frequency spectra are calculated fora plurality of regions as illustrated in FIG. 3, and the calculatedfrequency spectra are averaged to obtain the ultimate frequencyspectrum. However, the frequency spectrum which is calculated for eachof the plurality of regions may be employed to determine the peak whichis the target of processing within each of the plurality of regions, andthe quality of the grid may be judged for each of the plurality ofregions. By adopting such a configuration, the quality of the gridrelated to fluctuations in grid density can be judged for each of theplurality of regions.

In addition, in the first embodiment described above, the peakdetermining unit 33 determines the peak which is to be the target ofprocessing. However, in the case that only one peak appears in thefrequency response, the frequency at which the peak becomes maximalwithin the frequency response is known, or the like, the first judgingunit 34 may measure the width of the peak within the frequency responsewithout determining the peak which is the target of processing, andjudge the quality of the grid based on the measured width of the peak.In addition, the first judging unit 34 may measure the widths of peakswithin frequency responses and judge the quality of the grid based onthe measured widths of the peaks in each of the plurality of regionswithout determining peaks which are to be targets of processing. In thiscase, the peak determining unit 33 illustrated in FIG. 2 will becomeunnecessary.

Next, a second embodiment of the present disclosure will be described.FIG. 8 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to the second embodiment, which isrealized by installing a grid quality judging program into a computer 2.Note that in FIG. 8, constituent elements which are the same as thoseillustrated in FIG. 2 are denoted with the same reference numerals, anddetailed descriptions thereof will be omitted. As illustrated in FIG. 8,the grid quality judging apparatus of the second embodiment differs fromthe first embodiment in that it is equipped with a harmonic frequencycalculating unit 35 that calculates the frequency of at least oneharmonic which is generated based on the grid density and the Nyquistfrequency of the radiation image G0 and a second judging unit 36 thatcompares the frequency of a peak within the frequency spectrum and thefrequency of the at least one harmonic calculated by the harmonicfrequency calculating unit 35 and judges the quality of the grid basedon the presence or absence of peaks at frequencies different from thefrequency of the harmonic, instead of the peak determining unit 33 andthe first judging unit 34.

The harmonic frequency calculating unit 35 calculates the frequency ofthe at least one harmonic. In the case that there is only one harmonicfrequency to be calculated, the frequency of the first harmonic iscalculated, and in the case that there are a plurality of harmonicfrequencies to be calculated, the frequencies of a first harmonicthrough an Mth harmonic are calculated. Note that the value of M may beapproximately 3, for example. Here, the grid density of the grid 4 isknown. In addition, the Nyquist frequency of the radiation image G0 isalso known. In the case that the grid density is less than or equal tothe Nyquist frequency, the frequency of the first hannonic is equal tothe grid density. When calculating the frequency of the Mth harmonic,first, the grid density N is employed to calculate N*M. In the case thatthe value of N*M is less than or equal to the Nyquist frequency of theradiation image G0, the value of N*M corresponds to the frequency of theMth harmonic. The harmonic frequency calculating unit 35 calculates thefrequency of the Mth harmonic in this manner.

On the other hand, in the case that the grid density is greater than theNyquist frequency of the radiation image G0, the frequency responsetoward the high frequency side is folded back to the low frequency side.For this reason, the harmonic frequency calculating unit 35 calculatesthe frequency of the Mth harmonic by Formula (2) below, employing thegrid density and the Nyquist frequency. Note that Fin is the frequencyof the Mth harmonic, Fn is the Nyquist frequency, N is the grid density,and a is an arbitrary integer that includes 0. Here, the grid densityand the Nyquist density may be obtained by input via the input unit 8.Alternatively, the grid density and the Nyquist frequency of theradiation image G0 may be stored in the storage 23, the harmonicfrequency calculating unit 35 may read out the grid density and theNyquist frequency of the radiation image G0 from the storage 23, andperform calculations employing Formula (2), to calculate the frequencyof the Mth harmonic.

Fm=N*M−2*a*Fn (in the case tha (2*a+1)*Fn>N*M>2*a*Fn)

Fm=2*(a+1)*Fn−N*M (in the case that 2*(a+1)*Fn>N*M>(2*a+1)*Fn)   (2)

Note that Formula (2) calculates the frequency of the Mth harmonic fromthe grid density N. Alternatively, the frequency F1 of the firstharmonic may be employed to calculate the frequency of the Mth harmonicby Formula (3) below, in the case that the frequency F1 of the firstharmonic is known.

Fm=F1*M−2*a*Fn (in the case that (2*a+1)*Fn>F1*M>2*a*Fn)

Fm=2*(a+1)*Fn−F1*M (in the case that 2*(a+1)*Fn>F1*M>(2*a+1)*Fn)   (3)

The second judging unit 36 compares the frequency of the peak within thefrequency spectrum and the frequency of the at least one harmoniccalculated by the harmonic frequency calculating unit 35, and judges thequality of the grid based on the presence or absence of a peak at afrequency different from the frequency of the harmonic. Here, in thecase that a periodic structure different from the intended periodicstructure of the grid is not present, the frequency of the peak includedin the frequency spectrum will match the calculated frequency of theharmonic. On the other hand, in the case that that a periodic structuredifferent from the intended periodic structure of the grid is present asillustrated in FIG. 9, a peak will appear in the frequency spectrum at afrequency other than the calculated frequency of the harmonic.

Specifically, in the case that a periodic structure different from theintended periodic structure of the grid is not present in the grid 4,three peaks appear in the frequency response at the first through thirdharmonics which are generated by the intended periodic structure of thegrid, as illustrated in FIG. 4. The frequencies of the three harmonicsare the same as the frequencies of first through third harmonics whichare calculated by the harmonic frequency calculating unit 35. On theother hand, in the case that a periodic structure different from theintended periodic structure of the grid is present in the grid 4, a peakPa will appear in the frequency spectrum at a frequency other than thecalculated frequencies of the harmonics as illustrated in FIG. 10.

The second judging unit 36 compares the frequencies of the peaks withinthe frequency spectrum and the frequencies of the M harmonics, andjudges the quality of the grid based on the presence or absence of peaksat frequencies other than the frequencies of the M harmonics.Specifically, the second judging unit 36 detects the frequencies of allof the peaks within the frequency response. Then, the second judgingunit 36 judges whether a frequency, which is a target from among thefrequencies of the detected peaks, is within a predetermined thresholdvalue Th2 with respect to the calculated frequencies of all of theharmonics. Further, this judgment is performed for all of the peakswhich are detected within the frequency response. As a result, in thecase that a peak is present at a frequency which differs from thecalculated frequencies of the harmonics by a value greater than thethreshold value Th2, the grid includes an unnecessary periodic structurewhich is different from the intended structure of the grid, andtherefore the quality of the grid is judged to be poor. For example, ifa peak Pa appears at a frequency other than the frequencies of the peaksP1 through P3 of the first through third harmonics as illustrated inFIG. 10, the quality of the grid is judged to be poor. The judgmentresults are displayed by the display unit 6 in the same manner as in thefirst embodiment.

Next, the processes which are performed by the second embodiment will bedescribed. FIG. 11 is a flow chart that illustrates the processes whichare performed by the second embodiment. First, imaging of the grid 4 isperformed and the image obtaining unit 31 of the computer 2 obtains aradiation image G0 of the grid (step ST11). Then, the frequencyanalyzing unit 32 performs frequency analysis on the radiation image G0and obtains the frequency spectrum of the radiation image G0 (stepST12). Next, the harmonic frequency calculating unit 35 calculates thefrequency of at least one harmonic which is generated, based on the griddensity and the Nyquist frequency of the radiation image G0 (step ST13).Further, the second judging unit 36 compares the frequencies of peakswithin the frequency spectrum and the calculated frequency of the atleast one harmonic, judges the quality of the grid 4 based on thepresence or absence of peaks at frequencies other than the frequenciesof the harmonics (step ST14), and the process ends. The judgment resultsare displayed by the display unit 6.

As described above, the second embodiment compares the frequencies ofthe peaks in the frequency spectrum with the calculated frequencies ofthe at least one harmonic calculated by the harmonic frequencycalculating unit 35, and judges the quality of the grid based on thepresence or absence of peaks at frequencies different from thefrequencies of the harmonics. Therefore, the quality of the grid relatedto periodic structures different from the intended periodic structure ofthe grid can be easily judged.

Note that in the second embodiment, frequency spectra are calculated fora plurality of regions as illustrated in FIG. 3, and the calculatedfrequency spectra are averaged to obtain the ultimate frequencyspectrum. However, the frequency spectrum which is calculated for eachof the plurality of regions may be employed to judge the quality of thegrid for each of the plurality of regions. By adopting such aconfiguration, the quality of the grid related to periodic structuresdifferent from the intended periodic structure of the grid can be judgedfor each of the plurality of regions.

Next, a third embodiment of the present disclosure will be described.FIG. 12 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to the third embodiment, which isrealized by installing a grid quality judging program into a computer 2.Note that in FIG. 12, constituent elements which are the same as thoseillustrated in FIG. 2 are denoted with the same reference numerals, anddetailed descriptions thereof will be omitted. As illustrated in FIG.12, the grid quality judging apparatus of the third embodiment differsfrom the first embodiment in that the frequency analyzing unit 32performs frequency analysis in a first and a second direction which areperpendicular to each other within the radiation image G0 to obtain afrequency spectrum for each of the first and second directions, and thatthe grid judging apparatus is equipped with a peak presence detectingunit 37 that detects the presence or absence of peaks in the frequencyspectra of the first and second directions and a third judging unit 38that judges the quality of the grid based on the presence or absence ofpeaks, instead of the peak determining unit 33 and the first judgingunit 34.

Here, when imaging is performed employing the grid 4, the grid 4 isarranged such that the vertical direction or the horizontal direction ofthe obtained radiation image G0 matches the direction of the strips ofthe grid 4. The first and second directions which are perpendicular toeach other within the radiation image G0 refer to a direction thatmatches the direction of the stripes of the grid 4 and a directionperpendicular to the direction of the stripes of the grid 4, within theradiation image G0.

FIG. 13 is a diagram for explaining frequency analysis which isperformed by the third embodiment. In the case that the stripes of thegrid 4 are parallel to the long side of the radiation detector 5 duringimages as illustrated in FIG. 13, a periodic pattern which isperiodically arranged in the direction parallel to the long side, thatis, the x direction in FIG. 13, is included in the radiation image G0.In the third embodiment, the frequency analyzing unit 32 performsfrequency analysis in the direction perpendicular to and the directionparallel to the stripes of the grid 4, to obtain two frequency spectra.Specifically, the x direction is designated as the first direction andthe y direction is designated as the second direction as illustrated inFIG. 13, and frequency analysis is performed on the radiation image G0in a region in the first direction indicated by the arrow 41 and in aregion in the second direction indicated by the arrow 42 by Fouriertransform or high speed Fourier transform, to obtain a first and secondfrequency spectra in the x direction and the y direction of theradiation image G0. At this time, the frequency spectra may becalculated for a plurality of linear regions in the x direction and they direction, the frequency spectra obtained in these regions may beaveraged and obtained as ultimate first and second frequency spectra.

Here, if periodic structures in a direction different from that of thestripes of the grid are not included in the grid 4 as illustrated inFIG. 3, peaks will be included in only one of the frequency spectrawhich are obtained for each of the first and second directions, whichare perpendicular to each other within the radiation image G0.Specifically, the frequency spectrum which is calculated in the xdirection illustrated in FIG. 13 will be that having peaks atfrequencies corresponding to the intended periodic structure of thegrid, as illustrated in FIG. 3. In addition, no peaks will appear in thefrequency spectrum which is calculated in the y direction as illustratedin FIG. 14.

On the other hand, in the case that a periodic structure in a directiondifferent from the stripes of the grid is included in the grid 4 asillustrated in FIG. 15, a peak Pb will appear in the frequency spectrumwhich is calculated in the y direction as well, as illustrated in FIG.16.

At this time, the sizes of the peaks differ in the direction of thestripes of the grid and the direction different therefrom. Therefore, itis possible to recognize which of the first and second directions thedirections of the stripes is. For this reason, the peak presencedetecting unit 37 detects the presence of peaks in each of the frequencyspectra in the first and second directions. The third judging unit 38judges the quality of the grid based on the presence of peaks in thefrequency spectra in the first and second directions. Specifically, thethird judging unit 38 judges that the quality of the grid is poor in thecase that a peak appears in the frequency spectrum in a directiondifferent from the direction of the stripes of the grid.

Next, the processes which are performed by the third embodiment will bedescribed. FIG. 17 is a flow chart that illustrates the processes whichare performed by the third embodiment. First, imaging of the grid 4 isperformed and the image obtaining unit 31 of the computer 2 obtains aradiation image G0 of the grid (step ST21). Then, the frequencyanalyzing unit 32 performs frequency analysis on the radiation image G0and obtains the frequency spectrum of the radiation image G0 in each ofthe first and second directions (step ST22). Next, the peak presencedetecting unit 37 detects the presence or absence of peaks in thefrequency spectra of the first and second directions (step ST23).Thereafter, the third judging unit 38 judges the quality of the grid 4based on the presence or absence of peaks in the frequency spectrum ofeach of the first and second directions (step ST24), and the processends. The judgment results are displayed by the display unit 6.

As described above, the third embodiment judges the quality of the gridbased on the presence of peaks in the frequency spectrum of each of thefirst and second directions. Therefore, the quality of the grid relatedto periodic structures which are present in a direction different fromthe direction of the stripes of the grid can be easily judged.

Note that in the third embodiment, the frequency spectra are calculatedfor the radiation image G0 in the regions of the arrow 41 in the firstdirection and the arrow 42 in the second direction, to judge the qualityof the grid. Alternatively, the radiation image G0 may be divided into aplurality of regions, for example, four equal parts, and the quality ofthe grid may be judged for each of the plurality of regions based on thepresence or absence of peaks in the frequency spectra of the first andsecond directions within each of the regions. Thereby, the quality ofthe grid related to periodic structures which are present in a directiondifferent from the direction of the stripes of the grid can be easilyjudged within each of a plurality of regions.

Next, a fourth embodiment of the present disclosure will be described.FIG. 18 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to the fourth embodiment, which isrealized by installing a grid quality judging program into a computer 2.Note that in FIG. 18, constituent elements which are the same as thoseillustrated in FIG. 2 are denoted with the same reference numerals, anddetailed descriptions thereof will be omitted. As illustrated in FIG.18, the grid quality judging apparatus of the fourth embodiment differsfrom the first embodiment in that it is equipped with the harmonicfrequency calculating unit 35 and the second judging unit 36 of thesecond embodiment, in addition to the constituent elements of the gridquality judging apparatus of the first embodiment.

As described above, the fourth embodiment is equipped with the firstjudging unit 34 of the first embodiment and the second judging unit 36of the second embodiment. Therefore, both the quality of the gridrelated to fluctuations in grid density and the quality of the gridrelated to periodic structures different from the intended periodicstructure of the grid can be easily judged.

Next, a fifth embodiment of the present disclosure will be described.FIG. 19 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to the fifth embodiment, which isrealized by installing a grid quality judging program into a computer 2.Note that in FIG. 19, constituent elements which are the same as thoseillustrated in FIG. 2 are denoted with the same reference numerals, anddetailed descriptions thereof will be omitted. As illustrated in FIG.19, the grid quality judging apparatus of the fifth embodiment differsfrom the first embodiment in that it is equipped with the peak presencedetecting unit 37 and the third judging unit 38 of the third embodiment,in addition to the constituent elements of the grid quality judgingapparatus of the first embodiment. Note that in the fifth embodiment,the frequency analyzing unit 32 obtains frequency spectra for each ofthe first and second directions in the radiation image G0 in the samemanner as the third embodiment.

As described above, the fifth embodiment is equipped with the firstjudging unit 34 of the first embodiment and the third judging unit 38 ofthe second embodiment. Therefore, both the quality of the grid relatedto fluctuations in grid density and the quality of the grid related toperiodic structures which are present in a direction different from thedirection of the stripes of the grid can be easily judged.

Next, a sixth embodiment of the present disclosure will be described.FIG. 20 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to the sixth embodiment, which isrealized by installing a grid quality judging program into a computer 2.Note that in FIG. 20, constituent elements which are the same as thoseillustrated in FIG. 2 are denoted with the same reference numerals, anddetailed descriptions thereof will be omitted. As illustrated in FIG.20, the grid quality judging apparatus of the sixth embodiment differsfrom the first embodiment in that it is equipped with the peak presencedetecting unit 37 and the third judging unit 38 of the third embodiment,in addition to the constituent elements of the grid quality judgingapparatus of the second embodiment. Note that in the sixth embodiment,the frequency analyzing unit 32 obtains frequency spectra for each ofthe first and second directions in the radiation image G0 in the samemanner as the third embodiment.

As described above, the sixth embodiment is equipped with the secondjudging unit 36 of the second embodiment and the third judging unit 38of the third embodiment. Therefore, the quality of the grid related toperiodic structures different from the intended periodic structure ofthe grid and the quality of the grid related to periodic structureswhich are present in a direction different from the direction of thestripes of the grid can both be easily judged.

Next, a seventh embodiment of the present disclosure will be described.FIG. 21 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to the seventh embodiment, which isrealized by installing a grid quality judging program into a computer 2.Note that in FIG. 21, constituent elements which are the same as thoseillustrated in FIG. 2 are denoted with the same reference numerals, anddetailed descriptions thereof will be omitted. As illustrated in FIG.21, the grid quality judging apparatus of the seventh embodiment differsfrom the first embodiment in that it is equipped with the harmonicfrequency calculating unit 35 and the second judging unit 36 of thesecond embodiment, as well as the peak presence detecting unit 37 andthe third judging unit 38 of the third embodiment, in addition to theconstituent elements of the grid quality judging apparatus of the firstembodiment. Note that in the seventh embodiment, the frequency analyzingunit 32 obtains frequency spectra for each of the first and seconddirections in the radiation image G0 in the same manner as the thirdembodiment.

As described above, the seventh embodiment is equipped with the firstjudging unit 24 of the first embodiment, the second judging unit 36 ofthe second embodiment, and the third judging unit 38 of the thirdembodiment. Therefore, the quality of the grid related to fluctuationsin grid density, the quality of the grid related to periodic structuresdifferent from the intended periodic structure of the grid, and thequality of the grid related to periodic structures which are present ina direction different from the direction of the stripes of the grid canall be easily judged.

Next, an eighth embodiment of the present disclosure will be described.FIG. 22 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to the eighth embodiment, which isrealized by installing a grid quality judging program into a computer 2.Note that in FIG. 22, constituent elements which are the same as thoseillustrated in FIG. 2 are denoted with the same reference numerals, anddetailed descriptions thereof will be omitted. As illustrated in FIG.22, the grid quality judging apparatus of the eighth embodiment differsfrom the first embodiment in that it is equipped with a first qualitydata generating unit 50 that generates quality data representing thequality of the grid, instead of the first judging unit 34 of the gridquality judging apparatus of the first embodiment.

The first quality data generating unit 50 measures the half value athalf width of a peak which is determined to be a target of processing,generates the measured width of the peak which is determined to be thetarget of processing as quality data Q0, and outputs the quality data Q0to the display unit 6. FIG. 23 is a diagram that illustrates the qualitydata Q0 which is displayed by the display unit 6 in the eighthembodiment. As illustrated in FIG. 23, the value of the half value athalf width of the peak which is determined to be target of processing isdisplayed by the display unit 6 as the quality data Q0. Note that thethreshold value Th1 of the first embodiment, against which the width ofthe peak is compared, may also be displayed by the display unit 6. InFIG. 23, the threshold value Th1 is also displayed along with the widthof the peak.

Next, the processes which are performed by the eighth embodiment will bedescribed. FIG. 24 is a flow chart that illustrates the processes whichare performed by the eighth embodiment. First, imaging of the grid 4 isperformed and the image obtaining nit 31 of the computer 2 obtains aradiation image G0 (step ST31). Then, the frequency analyzing unit 32performs frequency analysis on the radiation image G0 and obtains thefrequency spectrum of the radiation image G0 (step ST32). Next, the peakdetermining unit 33 determines the peak which will be a target ofprocessing within the frequency spectrum (step ST33). Then, the firstquality data generating unit 50 measures the width of the peak which isthe target of processing, and generates quality data Q0 representing themeasured width of the peak, which is the target of processing (stepST34). Further, the display unit 6 displays the quality data Q0, and theprocess ends.

As described above, the eighth embodiment measures the width of the peakwhich is determined to be the target of processing within the frequencyspectrum, generates the quality data Q0 representing the measured widthof the peak which is the target of processing, and displays the qualitydata Q0 on the display unit 6. Therefore, an operator can easily judgethe quality of the grid related to fluctuations in grid density, basedon the displayed quality data Q0.

Note that in the eighth embodiment, frequency spectra may be calculatedfor a plurality of regions, the frequency spectrum which is calculatedfor each of the plurality of regions may be employed to determine thepeak which is the target of processing within each of the plurality ofregions, and the quality data Q0 may be generated for each of theplurality of regions. In this case, the quality data Q0, that is, thewidths of the peaks, may be displayed for each of the plurality ofregions. As the manner of display, a color map, in which regions aredisplayed in different colors according to the widths of the peaks, maybe displayed. FIG. 25 is a diagram that illustrates an example of such acolor map. Note that in FIG. 25, different hatching indicates differentcolors. By adopting such a configuration, an operator can judge thequality of the grid related to fluctuations in grid density for each ofthe plurality of regions.

In addition, in the eighth embodiment described above, the peakdetermining unit 33 determines the peak which is to be the target ofprocessing. However, in the case that only one peak appears in thefrequency response, the frequency at which the peak becomes maximalwithin the frequency response is known, or the like, the first qualitydata generating unit 50 may measure the width of the peak within thefrequency response without determining the peak which is the target ofprocessing, and cause the measured width to be displayed as the qualitydata Q0. In addition, the first quality data generating unit 50 maymeasure the widths of peaks within frequency responses and cause themeasured width to be displayed as the quality data Q0 in each of theplurality of regions without determining peaks which are to be targetsof processing. In this case, the peak determining unit 33 illustrated inFIG. 22 will become unnecessary.

Next, a ninth embodiment of the present disclosure will be described.FIG. 26 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to the ninth embodiment, which isrealized by installing a grid quality judging program into a computer 2.Note that in FIG. 26, constituent elements which are the same as thoseillustrated in FIG. 8 are denoted with the same reference numerals, anddetailed descriptions thereof will be omitted. As illustrated in FIG.26, the grid quality judging apparatus of the ninth embodiment differsfrom the second embodiment in that it is equipped with a second qualitydata generating unit 51 that generates quality data representing thequality of the grid, instead of the second judging unit 36 of the gridquality judging apparatus of the second embodiment.

The second quality data generating unit 51 compares the frequency of thepeak within the frequency spectrum and the frequency of the at least oneharmonic calculated by the harmonic frequency calculating unit 35,generates the presence or absence of a peak at a frequency differentfrom the frequency of the harmonic as quality data Q1, and outputs thegenerated quality data Q1 to the display unit 6. Specifically, thesecond quality data generating unit 51 detects the frequencies of all ofthe peaks within the frequency response. Then, the second quality datagenerating unit 51 judges whether a frequency, which is a target fromamong the frequencies of the detected peaks, is within a predeterminedthreshold value Th2 with respect to the calculated frequencies of all ofthe harmonics. Further, this judgment is performed for all of the peakswhich are detected within the frequency response. As a result, in thecase that a peak is present at a frequency which differs from thecalculated frequencies of the harmonics by a value greater than thethreshold value Th2, the second quality data generating unit 51generates data indicating that a peak is present at a frequency whichdiffers from the frequencies of the harmonics as the quality data Q1. Onthe other hand, in the case that no peaks of frequencies that differfrom the calculated frequencies of the harmonics by a value greater thanthe threshold value Th2 appear, the second quality data generating unit51 generates data indicating that no peaks are present at frequenciesthat differ from the frequencies of the harmonics as the quality dataQ1. The display unit 6 displays the quality data Q1.

FIG. 27 is a diagram that illustrates the quality data Q1 which isdisplayed by the display unit 6 in the ninth embodiment. As illustratedin FIG. 27, the display unit 6 displays whether a peak is present orabsent at a frequency different from the frequencies of the harmonics asthe quality data Q1. Note that in FIG. 27, text reading “Peak Present”is displayed.

As described above, the ninth embodiment compares the frequencies of thepeaks in the frequency spectrum with the calculated frequencies of theat least one harmonic calculated by the harmonic frequency calculatingunit 35, generates data representing the presence or absence of peaks atfrequencies different from the frequencies of the harmonics as thequality data Q1, and displays the quality data Q1 on the display unit 6.Therefore, an operator can easily judge the quality of the grid relatedto periodic structures different from the intended periodic structure ofthe grid, based on the displayed quality data Q1.

Note that in the ninth embodiment, frequency spectra which arecalculated for each of a plurality of regions may be employed todetermine peaks which are to be targets of processing and to generatethe quality data Q1, for each of the plurality of regions. In this case,the quality data Q1, that is, the presence or absence of the peaks, maybe displayed for each of the plurality of regions. As the manner ofdisplay, a color map, in which regions are displayed in different colorsaccording to the presence or absence of the peaks, may be displayed. Byadopting such a configuration, an operator can judge the quality of thegrid related to periodic structures different from the intended periodicstructure of the grid for each of the plurality of regions.

Next, a tenth embodiment of the present disclosure will be described.FIG. 28 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to the tent embodiment, which isrealized by installing a grid quality judging program into a computer 2.Note that in FIG. 28, constituent elements which are the same as thoseillustrated in FIG. 12 are denoted with the same reference numerals, anddetailed descriptions thereof will be omitted. As illustrated in FIG.28, the grid quality judging apparatus of the tenth embodiment differsfrom the third embodiment in that it is equipped with a third qualitydata generating unit 52 that generates quality data representing thequality of the grid, instead of the third judging unit 38 of the gridquality judging apparatus of the third embodiment.

The third quality data generating unit 52 generates quality data Q2representing the presence or absence of peaks within frequency spectrafor both a first and second direction, and outputs the quality data Q2to the display unit 6. The display unit 6 displays the quality data Q2.

FIG. 29 is a diagram that illustrates the quality data Q2 which isdisplayed by the display unit 6 in the tenth embodiment. As illustratedin FIG. 29, the display unit 6 displays the presence or absence of peaksin the frequency spectrum of each of the first and second directions asthe quality data Q2. Note that in FIG. 29, text reading “Peak Present”is displayed with respect to the first direction, and text reading “NoPeak Present” is displayed with respect to the second direction.

As described above, the tenth embodiment generates data representing thepresence or absence of peaks in the frequency spectrum of each of thefirst and second directions as the quality data Q2, and causes thequality data Q2 to be displayed by the display unit 6. Therefore, anoperator can easily judge the quality of the grid related to periodicstructures which are present in a direction different from the directionof the stripes of the grid, based on the displayed quality data Q2.

Note that in the tenth embodiment, the radiation image G0 may be dividedinto a plurality of regions, for example, four equal parts, and thequality data Q2 representing the quality of the grid may be generatedfor each of the plurality of regions based on the presence or absence ofpeaks in the frequency spectra of the first and second directions withineach of the regions. In this case, the quality data Q2 , that is, thepresence or absence of peaks in the first and second directions, may bedisplayed for each of the regions. As the manner of display, a color mapin which the colors of regions differ according to the presence orabsence of peaks in the first and second directions may be displayed.For example, a region may be colored green in the case that a peak ispresent only in the first direction, and colored red in the case thatpeaks are present in both the first and second directions. Thereby, anoperator can judge the quality of the grid related to periodicstructures which are present in a direction different from the directionof the stripes of the grid within each of a plurality of regions.

Next, an eleventh embodiment of the present disclosure will bedescribed. FIG. 30 is a diagram that illustrates the schematic structureof a grid quality judging apparatus according to the eleventhembodiment, which is realized by installing a grid quality judgingprogram into a computer 2. Note that in FIG. 30, constituent elementswhich are the same as those illustrated in FIG. 22 are denoted with thesame reference numerals, and detailed descriptions thereof will beomitted. As illustrated in FIG. 30, the grid quality judging apparatusof the eleventh embodiment differs from the eighth embodiment in that itis equipped with the harmonic frequency calculating unit 35 and thesecond quality data generating unit 51 of the ninth embodiment, inaddition to the constituent elements of the grid quality judgingapparatus of the eighth embodiment, and in that the display unit 6 isconfigured to display quality data Q0 and Q1.

As described above, the eleventh embodiment is equipped with the firstquality data generating unit 50 of the eighth embodiment and the secondquality data generating unit 51 of the ninth embodiment. Therefore, anoperator can easily judge both the quality of the grid related tofluctuations in grid density and the quality of the grid related toperiodic structures different from the intended periodic structure ofthe grid, by referring to the quality data Q0 and Q1 which are displayedby the display unit 6.

Next, a twelfth embodiment of the present disclosure will be described.FIG. 31 is a diagram that illustrates the schematic structure of a gridquality judging apparatus according to the twelfth embodiment, which isrealized by installing a grid quality judging program into a computer 2.Note that in FIG. 31, constituent elements which are the same as thoseillustrated in FIG. 22 are denoted with the same reference numerals, anddetailed descriptions thereof will be omitted. As illustrated in FIG.31, the grid quality judging apparatus of the twelfth embodiment differsfrom the eighth embodiment in that it is equipped with the peak presencedetecting unit 37 and the third quality data generating unit 52 of thetenth embodiment, in addition to the constituent elements of the gridquality judging apparatus of the eighth embodiment, and in that thedisplay unit 6 is configured to display quality data Q0 and Q2. Notethat in the twelfth embodiment, the frequency analyzing unit 32 obtainsfrequency spectra for each of the first and second directions in theradiation image G0 in the same manner as the tenth embodiment.

As described above, the twelfth embodiment is equipped with the firstquality data generating unit 50 of the eighth embodiment and the thirdquality data generating unit 52 of the eighth embodiment. Therefore, andoperator can easily judge both the quality of the grid related tofluctuations in grid density and the quality of the grid related toperiodic structures which are present in a direction different from thedirection of the stripes of the grid, by referring to the quality dataQ0 and Q2 which are displayed by the display unit 6.

Next, a thirteenth embodiment of the present disclosure will bedescribed. FIG. 32 is a diagram that illustrates the schematic structureof a grid quality judging apparatus according to the thirteenthembodiment, which is realized by installing a grid quality judgingprogram into a computer 2. Note that in FIG. 32, constituent elementswhich are the same as those illustrated in FIG. 26 are denoted with thesame reference numerals, and detailed descriptions thereof will beomitted. As illustrated in FIG. 32, the grid quality judging apparatusof the thirteenth embodiment differs from the tenth embodiment in thatit is equipped with the peak presence detecting unit 37 and the thirdquality data generating unit 52 of the tenth embodiment, in addition tothe constituent elements of the grid quality judging apparatus of theninth embodiment, and in that the display unit 6 is configured todisplay quality data Q1 and Q2. Note that in the thirteenth embodiment,the frequency analyzing unit 32 obtains frequency spectra for each ofthe first and second directions in the radiation image G0 in the samemanner as the tenth embodiment.

As described above, the thirteenth embodiment is equipped with thesecond quality data generating unit 51 of the ninth embodiment and thethird quality data generating unit 52 of the tenth embodiment.Therefore, an operator can easily judge both the quality of the gridrelated to periodic structures different from the intended periodicstructure of the grid and the quality of the grid related to periodicstructures which are present in a direction different from the directionof the stripes of the grid, by referring to the quality data Q1 and Q2which are displayed by the display unit 6.

Next, a fourteenth embodiment of the present disclosure will bedescribed. FIG. 33 is a diagram that illustrates the schematic structureof a grid quality judging apparatus according to the seventh embodiment,which is realized by installing a grid quality judging program into acomputer 2. Note that in FIG. 33, constituent elements which are thesame as those illustrated in FIG. 22 are denoted with the same referencenumerals, and detailed descriptions thereof will be omitted. Asillustrated in FIG. 33, the grid quality judging apparatus of thefourteenth embodiment differs from the eighth embodiment in that it isequipped with the harmonic frequency calculating unit 35 and the secondquality data generating unit 51 of the ninth embodiment, as well as thepeak presence detecting unit 37 and the third quality data generatingunit 52 of the tenth embodiment, in addition to the constituent elementsof the grid quality judging apparatus of the eighth embodiment, and inthat the display unit 6 is configured to display quality data Q0, Q1,and Q2. Note that in the fourteenth embodiment, the frequency analyzingunit 32 obtains frequency spectra for each of the first and seconddirections in the radiation image G0 in the same manner as the tenthembodiment.

As described above, the fourteenth embodiment is equipped with the firstquality data generating unit 50 of the eighth embodiment, the secondquality data generating unit 51 of the ninth embodiment, and the thirdquality data generating unit 52 of the tenth embodiment. Therefore, anoperator can easily judge all of the quality of the grid related tofluctuations in grid density, the quality of the grid related toperiodic structures different from the intended periodic structure ofthe grid, and the quality of the grid related to periodic structureswhich are present in a direction different from the direction of thestripes of the grid, by referring to the quality data Q0, Q1, and Q2which are displayed by the display unit 6.

Note that in each of the embodiments described above, radiation imageswhich are obtained by systems that employ the radiation detector 5 toobtain radiation images of subjects are employed to perform scatteredray removing processes. However, it goes without saying that the presentdisclosure can be applied to cases in which radiation images, which areobtained by recording radiation image data in a stimulable phosphorsheet as a radiation detector as disclosed in Japanese Unexamined PatentPublication No. H8-266529, H9-22039, etc. and then photoelectricallyread out from the stimulable phosphor sheet, are employed as well.

Hereinafter, the operative effects of the embodiments of the presentdisclosure will be described.

If there are no fluctuations in the grid density, a peak will onlyappear in a frequency response at a frequency that corresponds to theintended periodic structure of the grid, and therefore the width of thepeak which is the target of processing will be small. On the other hand,in the case that there are fluctuations in the grid density, peaks willappear at frequencies different from the frequency of the intendedperiodic structure of the grid, in addition to the peak at the frequencyof the intended periodic structure of the grid. In addition, these twofrequencies will not differ greatly, and the values thereof will becomparatively close. As a result, the peaks of the two frequencies willoverlap, and the width of the peak which is the target of processingwithin the frequency response will become great. Accordingly, the widthof the peak which is the target of processing corresponds to the size offluctuations in the grid density. That is, the fluctuations in griddensity will be smaller as the width of the peak is smaller. For thisreason, the quality of the grid related to fluctuations in the griddensity can be easily judged by measuring the width of the peak andjudging the quality of the grid based on the measured width of the peakor by generating quality data that represents the width of the peak anddisplaying the quality data. For example, the width of the peak may becompared with a threshold value, and the quality of the grid may bejudged to be poor if the width of the peak is greater than or equal tothe threshold value.

The quality of the grid related to fluctuations in the grid density canbe judged for each region of the grid, by dividing the radiation imageinto a plurality of regions, obtaining frequency spectra, determiningpeaks which are to be targets of processing, and judging the quality ofthe grid or generating and displaying quality data for each of thedivided regions.

In the case that a periodic structure different from the intendedperiodic structure of the grid is not present, the frequency of the peakincluded in the frequency spectrum will match the calculated frequencyof the harmonic. On the other hand, in the case that that a periodicstructure different from the intended periodic structure of the grid ispresent, a peak will appear in the frequency spectrum at a frequencyother than the calculated frequency of the harmonic. Therefore, bycomparing the frequencies of the peaks in the frequency spectrum withthe frequencies of harmonics, and judging the quality of the grid basedon the presence or absence of peaks at frequencies different from thefrequencies of the harmonics or generating quality data representing thepresence or absence of such peaks, the quality of the grid related toperiodic structures different from the intended periodic structure ofthe grid can be easily judged. For example, the quality of a grid can bejudged to be poor in the case that a peak is present at a frequencyother than the frequencies of harmonics as a result of the comparison.

Here, if periodic structures in a direction different from that of thestripes of the grid are not included in the grid, peaks will be includedin only one of the frequency spectra which are obtained for each of thefirst and second directions, which are perpendicular to each otherwithin the radiation image. On the other hand, in the case that aperiodic structure in a direction different from the stripes of the gridis included in the grid, peaks will appear in the frequency spectraobtained for both the first and second directions. At this time, thesizes of the peaks differ in the direction of the stripes of the gridand the direction different therefrom. Therefore, it is possible torecognize which of the first and second directions the directions of thestripes is. Accordingly, the quality of the grid can be easily judged,by judging the quality of the grid based on the presence of peaks in thefrequency spectra in the first and second directions or by generatingquality data representing the presence or absence of peaks. For example,the quality of the grid may be judged to poor in the case that a peakappears in the frequency spectrum in a direction different from thedirection of the stripes of the grid.

What is claimed is:
 1. A grid quality judging apparatus comprising: afrequency analyzing unit configured to perform frequency analysis on aradiation image that includes a periodic pattern caused by a grid, toobtain a frequency spectrum of the radiation image; and a judging unitconfigured to judge the quality of the grid, based on peaks which areincluded in the frequency spectrum.
 2. A grid quality judging apparatusas defined in claim 1, wherein: the judging unit measures the widths ofthe peaks and judges the quality of the grid based on the measuredwidths of the peaks.
 3. A grid quality judging apparatus as defined inclaim 2, further comprising: a peak determining unit configured todetermine peaks within the frequency spectrum which will be targets ofprocessing; and wherein the judging unit measures the widths of thepeaks which are the targets of processing and judges the quality of thegrid based on the measured widths of the peaks which are the targets ofprocessing.
 4. A grid quality judging apparatus as defined in claim 2,wherein: the frequency analyzing unit divides the radiation image into aplurality of regions and obtain frequency spectra for each of theplurality of regions; and the judging unit measures the widths of peakswithin each of the plurality of regions, and judge the quality of thegrid in each of the plurality of grids based on the measured widths ofthe peaks within each of the plurality of regions.
 5. A grid qualityjudging apparatus as defined in claim 2, wherein: the frequencyanalyzing unit divides the radiation image into a plurality of regionsand obtain frequency spectra for each of the plurality of regions; thepeak determining unit determines peaks to be targets of processingwithin each of the plurality of regions; and the judging unit measuresthe widths of peaks which are targets of processing within each of theplurality of regions, and judges the quality of the grid in each of theplurality of regions based on the measured widths of the peaks which aretargets of processing within each of the plurality of regions.
 6. A gridquality judging apparatus as defined in claim 1, further comprising: aharmonic frequency calculating unit configured to calculate thefrequency of at least one harmonic which is generated based on the griddensity and the Nyquist frequency of the radiation image; and wherein:the judging unit compares the frequency of the peaks within thefrequency spectrum and the frequency of the at least one harmonic, andjudges the quality of the grid based on the presence or the absence of apeak at a frequency different from the frequency of the harmonic.
 7. Agrid quality judging apparatus as defined in claim 6, wherein: thefrequency analyzing unit divides the radiation image into a plurality ofregions and obtain frequency spectra for each of the plurality ofregions; the harmonic frequency calculating unit calculates thefrequency of at least one harmonic within each of the plurality ofregions; and the judging unit compares the frequency of the peaks withinthe frequency spectrum and the frequency of the at least one harmonic,and judges the quality of the grid based on the presence or the absenceof a peak at a frequency different from the frequency of the hannonicwithin each of the plurality of regions.
 8. A first grid quality judgingapparatus as defined in claim 1, wherein: the frequency analyzing unitobtains frequency spectra for each of a first and second direction whichare perpendicular to each other, by performing frequency analysis in thefirst and second directions within the radiation image: the grid qualityjudging apparatus further comprises: a peak presence detecting unitconfigured to detect the presence or absence of peaks within thefrequency spectra for the first and second directions; and the judgingunit judges the quality of the grid based on the presence or absence ofpeaks within the frequency spectra for the first and second directions.9. A grid quality judging apparatus as defined in claim 8, wherein thefrequency analyzing unit divides the radiation image into a plurality ofregions and obtains frequency spectra for the first and seconddirections within each of the plurality of regions; the peak presencedetecting unit detects the presence or absence of peaks within thefrequency spectra of each of the plurality of regions; and the judgingunit judges the quality of the grid based on the presence or absence ofpeaks within the frequency spectra for the first and second directionswithin each of the plurality of regions.
 10. A grid quality judgingapparatus comprising: a frequency analyzing unit configured to performfrequency analysis on a radiation image that includes a periodic patterncaused by a grid, to obtain a frequency spectrum of the radiation image;a quality data generating unit configured to generate quality data thatrepresents the quality of the grid, based on peaks which are included inthe frequency spectrum; and a display unit configured to display thequality data.
 11. A grid quality judging apparatus as defined in claim10, wherein: the quality data generating unit measures the widths of thepeaks and generates the quality data based on the measured widths of thepeaks.
 12. A grid quality judging apparatus as defined in claim 11,further comprising: a peak determining unit configured to determinepeaks within the frequency spectrum which will be targets of processing;and wherein: the quality data generating unit measures the widths of thepeaks which are the targets of processing and generates the quality databased on the measured widths of the peaks which are the targets ofprocessing.
 13. A grid quality judging apparatus as defined in claim 11,wherein: the frequency analyzing unit divides the radiation image into aplurality of regions and obtains frequency spectra for each of theplurality of regions; and the quality data generating unit measures thewidths of peaks within each of the plurality of regions, and generatesthe quality data for each of the plurality of grids based on themeasured widths of the peaks within each of the plurality of regions.14. A grid quality judging apparatus as defined in claim 12, wherein:the frequency analyzing unit divides the radiation image into aplurality of regions and obtain frequency spectra for each of theplurality of regions; the peak determining unit determines peaks to betargets of processing within each of the plurality of regions; and thequality data generating unit measures the widths of peaks which aretargets of processing within each of the plurality of regions, andgenerates the quality data for each of the plurality of regions based onthe measured widths of the peaks which are targets of processing withineach of the plurality of regions.
 15. A grid quality judging apparatusas defined in claim 10, further comprising: a harmonic frequencycalculating unit configured to calculate the frequency of at least oneharmonic which is generated based on the grid density and the Nyquistfrequency of the radiation image; and wherein: the quality datagenerating unit compares the frequency of the peaks within the frequencyspectrum and the frequency of the at least one harmonic, and generatesthe quality data based on the presence or the absence of a peak at afrequency different from the frequency of the harmonic.
 16. A gridquality judging apparatus as defined in claim 15, wherein: the frequencyanalyzing unit divides the radiation image into a plurality of regionsand obtains frequency spectra for each of the plurality of regions; theharmonic frequency calculating unit calculates the frequency of at leastone harmonic within each of the plurality of regions; and the qualitydata generating unit compares the frequency of the peaks within thefrequency spectrum and the frequency of the at least one harmonic andgenerates the quality data based on the presence or the absence of apeak at a frequency different from the frequency of the harmonic withineach of the plurality of regions.
 17. A grid quality judging apparatusas disclosed in claim 10, wherein: the frequency analyzing unit obtainsfrequency spectra for each of a first and second direction which areperpendicular to each other, by performing frequency analysis in thefirst and second directions within the radiation image; the grid qualityjudging apparatus further comprises a peak presence detecting unitconfigured to detect the presence or absence of peaks within thefrequency spectra for the first and second directions; and the qualitydata generating unit generates the quality data based on the presence orabsence of peaks within the frequency spectra for the first and seconddirections.
 18. A grid quality judging apparatus as defined in claim 17,wherein: the frequency analyzing unit divides the radiation image into aplurality of regions and obtains frequency spectra for the first andsecond directions within each of the plurality of regions; the peakpresence detecting unit detects the presence or absence of peaks withinthe frequency spectra of each of the plurality of regions; and thequality data generating unit generates the quality data based on thepresence or absence of peaks within the frequency spectra for the firstand second directions within each of the plurality of regions.
 19. Agrid quality judging method comprising: performing frequency analysis ona radiation image that includes a periodic pattern caused by a grid, toobtain a frequency spectrum of the radiation image; and judging thequality of the grid, based on peaks which are included in the frequencyspectrum.
 20. A grid quality judging method comprising: performingfrequency analysis on a radiation image that includes a periodic patterncaused by a grid, to obtain a frequency spectrum of the radiation image;generating quality data that represents the quality of the grid, basedon peaks which are included in the frequency spectrum; and displayingthe quality data.
 21. A non transitory recording medium having a gridquality judging program recorded therein, the grid quality judgingprogram causing a computer to execute the procedures of: performingfrequency analysis on a radiation image that includes a periodic patterncaused by a grid, to obtain a frequency spectrum of the radiation image;and judging the quality of the grid, based on peaks which are includedin the frequency spectrum.
 22. A non transitory recording medium havinga grid quality judging program recorded therein, the grid qualityjudging program causing a computer to execute the procedures of:performing frequency analysis on a radiation image that includes aperiodic pattern caused by a grid, to obtain a frequency spectrum of theradiation image; generating quality data that represents the quality ofthe grid, based on peaks which are included in the frequency spectrum;and displaying the quality data.